When manufacturing a three dimensional photonic device including several distinct micro-optical components, the more different the micro-optical components are from one another, the more difficult it is to integrate them in a single device, in an efficient and reliable way.
The integration of optical waveguides with free-space micro-optical components and micromechanical structures is a major technical problem because high positioning accuracy, cost efficiency, high yield and reliability have to be achieved. The integration scheme should also be compatible with a variety of optical and mechanical designs. A method that matches these conditions can pave the way for on-chip mode engineering, low-loss coupling of optical components with in-plane and out-of-plane components, and accurate alignment for packaging.
Hybrid integration is frequently used in order to package waveguides with lenses, mirrors and alignment structures. The major drawbacks of this approach are the increased cost due to the additional assembly steps and the limited accuracy of positioning.
Monolithic integration can potentially solve these problems. However, there are not any general purpose methods for monolithic integration of the three types of elements, namely guided wave photonic devices, free space micro-optical components and micromechanical structures. Even the application specific monolithic integration methods do not satisfy the stringent requirements mentioned above.
According to a first prior art, for example described in application US 2007/0116409A1, gradient-index (GRIN) lenses consisting of multiple layers that form a special distribution of refractive index, can be integrated with planar waveguides. However, fabrication of GRIN lenses is demanding due to the necessity of several layers with well-controlled refractive indices.
According to a second prior art, for example described in article which reference is “L. Y. Lin et al., IEEE Photon. Technol. Lett. 6. 1445-1447 (1994)”, three dimensional integrated micro-lenses can be fabricated using silicon micromachining, but this technique is compatible with only silicon-based material systems.
According to a third prior art, for example described in an article which reference is “F. E. Doany et al., IEEE Trans. Adv. Packag. 32, 345-359 (2009)”, or in article which reference is “A. L. Glebov et al., IEEE Photon. Technol. Lett. 17, 1540-1542 (2005)”, or in article which reference is “C. Choi et al., J. Lightwave Technol. 22, 2168-2176 (2004)”, or in article which reference is “M. Kagami et al., J. Lightwave Technol. 19, 1949-1955 (2001)”, or in article which reference is “T. Yoshimura et al., J. Lightwave Technol. 22, 2091-2100 (2004)”, several methods including laser ablation, dicing, blade cutting, reactive ion etching, and tilted exposure have been used to fabricate out-of-plane mirrors in polymer waveguides. However, these methods are limited to the fabrication of tilted plane mirrors.
According to a fourth prior art, for example described in application U.S. Pat. No. 7,092,602 B2 or in application US 2003/0215187 A1, grooves on the substrate for alignment of fibers with waveguides are reported. However, fabrication of grooves with micron-scale accuracy is not possible for some substrate materials.
According to a fifth prior art, for example described in application US 2009/0218519 A1, refractive index change based on two-photon absorption has also been proposed as a method to fabricate optical devices. However, only limited optical functionality can be achieved with this method because of the low refractive index contrast.
According to a sixth prior art, for example described in application US 2010/0142896 A1 or in article which reference is “N. Lindenmann et al., Optical Fiber Communication Conference, 2011, Paper PDPC1” or in document which can be found at following internet address
“http://www.eduprograms.seas.harvard.edu/reu05_papers/Barker_Krystal.pdf>>, there are other manufacturing methods using two photon absorption. But this prior art mounts components and connects them afterwards by direct laser writing the waveguides between these components.
According to a seventh prior art, for example described in article which reference is “Q.-D. Chen et al., CLEO/Pacific Rim Conference, 2009, 1-2,” there are methods of manufacturing individual optical elements, such as Fresnel lenses using two photon absorption. But, if the use of two-photon absorption for the fabrication of optical elements on polymers is known in itself, none of the previously cited prior art documents provides a solution based on two-photon absorption for building complex optical three dimensional structures, in an efficient and reliable way.